repair of DNA double-strand breaks. Other progeroid syndromes Bloom syndrome is a rare autosomal recessive disorder that is characterized by short stature, chromosomal instability, predisposition to cancer, and sun-sensitive skin. Those with Bloom syndrome can also have learning disabilities and have an increased risk of developing chronic obstructive pulmonary disease (COPD) and disease. Cockayne syndrome is a homozygous or heterozygous mutation that results in short stature, abnormalities in head size, and slow growth and development. Rothmund–Thomson syndrome is a rare autosomal recessive disorder that affects the skin. It is characterized by the sparse hair, juvenile cataracts, skeletal abnormalities, and stunted growth. Biogerontology Theories of ageing affect efforts to understand and find treatments for age-related conditions: Those who believe in the idea that ageing is an unavoidable side effect of some necessary function (antagonistic pleiotropy or disposable soma theories) logically tend to believe that attempts to delay ageing would result in unacceptable side effects to the necessary functions. Altering ageing is therefore "impossible", and study of ageing mechanisms is of only academic interest. Those believing in default theories of multiple maintenance mechanisms tend to believe that ways might be found to enhance the operation of some of those mechanisms. Perhaps they can be assisted by antioxidants or other agents. Those who believe in programmed ageing suppose that ways might be found to interfere with the operation of the part of the ageing mechanism that appears to be common to multiple symptoms, essentially "slowing down the clock" and delaying multiple manifestations. Such effect might be obtained by fooling a sense function. One such effort is an attempt to find a "mimetic" that would "mime" the anti-ageing effect of calorie restriction without having to actually radically restrict diet. See also List of life extension-related topics Negligible senescence Senescence Gerontology Phenoptosis References Further reading External links Evolutionary Theories of Aging and Longevity The Evolutionary Theory of Aging by João Pedro de Magalhães. Programmed-Aging.Org Site provides comprehensive information on programmed ageing, the programmed/non-programmed controversy, and underlying evolution controversies. How Evolutionary Thinking Affects People's Ideas About Aging Interventions AnAge Animal Ageing and Longevity Database Provides maximum observed ages and sexual maturity ages for many animals. The Case for Programmed Mammal Aging Describes empirical data, evolutionary rationale, and historical perspective supporting programmed ageing in mammals. Life Table for USA 2005 Probability of death as a function of age Life extension Evolutionary biology Senescence Theories of ageing Theories